Wednesday, June 9, 2010

Managing Rice Blast and Straighthead

The following questions have arisen repeatedly the last few days:


We have found blast lesions on CL 151 and CL 142 recently. How concerned should we be about each one and how should we manage to minimize neck blast later on each?


You should be more concerned about CL 151 than CL 142. CL 151 is very susceptible to neck blast and under favorable conditions, can be difficult to manage with respect to this disease. If leaf blast is found, or the field has a history of blast or has blast potential (erratic flood history, tree lines, river bottoms, sandy or other water percolating soil type) then you should pump up the field to a minimum 4 inch flood depth in the shallowest part of the field and try to maintain the rest of the season. If you find areas that are burning down from leaf blast, you should consider treating these regions (usually along edges or tree lines) with an application of Quadris, Quilt Xcel, Quilt, Gem or Stratego to minimize blast spore production for the field. If you are spraying the field for sheath blight anyway, the sheath blight application should suffice, depending on timing. If the field does not have hotspots, but only scattered leaf blast, this is not a step I would consider. CL 151 fields with any evidence of leaf blast should be sprayed twice to minimize neck blast, once at boot split and the second about a week later when the earliest heads are about 3/4 out of the boot. You should not cut rates either on this variety. Fields should be scouted extensively in June to mid July to determine leaf blast as lesions tend to disappear during boot to early heading for most observers.

CL 142 is less susceptible to blast in our limited experience than CL 151. It reacts more like Wells, so far. Again, pump up the field if leaf blast is found or in fields with a strong history or potential for blast. Fields like this should probably be sprayed at boot split for blast. Since this variety seems to behave like Wells, the second application and rates are subject to field judgment. If conditions are hot and dry, you can probably get by with less fungicide and perhaps one application. If this is the decision, make sure the fungicide application made is the boot split one, as it is more important. For both CL 151 and CL 142, this application is also appropriate for sheath blight control, if this disease has not been that aggressive earlier.

Is Taggart resistant to straighthead and how should it be treated to prevent this disease?


Based on two straighthead nurseries observed in 2009, we rated Taggart as resistant when compared to susceptible checks like Cocodrie and CL 131 (very susceptible). On typical fields, Taggart will likely not need to be drained or drained "dry to cracking", based on this experience. On fields with a very strong history of straighthead, it may be beneficial to drain most varieties, but resistant ones will not require as much drying as susceptible varieties, and the benefit will not be as great, obviously. On these fields, if it is raining to the degree that draining cannot be done, a variety like Taggart will still perform, whereas Cocodrie and the like will be devastated.

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